1. Technical Field of the Invention
The present invention relates generally to an engine start system which may be used in an idle stop system for automotive vehicles (also called an automatic engine stop/restart system) which works to stop an automotive engine automatically, for example, when the vehicle has stopped at an intersection or due to a traffic jam and then restart the engine when the vehicle driver performs a given starting operation (e.g., release of the driver's foot from the brake pedal).
2. Background Art
Automotive vehicles equipped with an automatic engine stop/restart system (also called an idle stop system) designed to stop the engine automatically when an output of the engine is not required and restart the engine automatically when the engine output is requested are expected to increase in order to reduce carbon dioxide emissions or increase the fuel economy.
The idle stop system typically works to automatically cut a supply of fuel to the engine to stop it, for example, when the vehicle stops at a red light at an intersection or in a traffic jam and then restart the engine when given restart requirements are met, e.g., the driver has released the brake pedal and/or shifted a selector lever to a drive range in the automatic transmission. For example, Japanese Patent First Publication No. 2003-301765 discloses such an idle stop system.
The vehicle operator may require the start of the vehicle immediately after the idle stop system has been activated to stop the engine, after which the vehicle stops. In such an event, if it is impossible to restart the engine until it stops completely, which may cause inconvenience to trailing vehicles. This may lead to the discomfort of the vehicle operator. One of requirements the idle stop system is needed to meet is, therefore, to enable the restart of the engine during deceleration thereof before being stopped completely.
In order to meet the above requirement, Japanese Patent First Publication No. 2005-330813 teaches an idle stop system which, when an engine restart request is made during a period of time in which the speed of the engine is decreasing before the engine stops completely, starts energization of a shunt coil to rotate a pinion gear and then brings the pinion gear into engagement with a ring gear installed on a crankshaft of the engine at the time when the rotation of the pinion gear is synchronized with that of the ring gear.
Additionally, Japanese Patent First Publication No. 2007-107527 teaches an idle stop system designed to bring the pinion gear into engagement with the ring gear when the speed of the internal combustion engine falls in a range between given maximum and minimum speeds, and the direction of rotation of the engine matches the forward direction of the crankshaft of the engine.
The idle stop system of Japanese Patent First Publication No. 2005-330813, as described above, requires the synchronization of the speed of the pinion gear with that of the ring gear and thus has the problem that the speed of the engine may drop before an engine starter starts rotating, which results in failure in the synchronization in a very low engine speed range. Moreover, when the idle stop system cuts the fuel to the engine, it usually causes the speed of the engine to drop rapidly and overshoot the zero. The engine then swings in the reverse and forward directions cyclically and eventually stops. In such a speed range where the engine swings (which will be referred to as an engine swing range below), it is very difficult to synchronize the speed of the pinion gear with that of the ring gear. The engagement between the pinion gear and the ring gear will also result in a great deal of mechanical impact between them, which may cause the breakage of the ring gear.
The idle stop system of Japanese Patent First Publication No. 2007-107527 is, as described above, designed to engage the pinion gear with the ring gear only when the direction of rotation of the engine matches the forward direction of the crankshaft of the engine, thus requiring a sensor to measure the direction of rotation of the engine. The system is inhibited from engaging the pinion gear with the ring gear when the engine is rotating in the reverse direction, thus resulting in an increased difficulty in engaging the pinion gear with the ring gear in the engine swing range.